1. Field of the Invention
The present invention relates generally to a method and apparatus for laminating lengths of material together, and, more particularly, wherein rollers carry the lengths of material.
2. Brief Description of the Prior Art
Forming layered or laminated material products by the use of a plurality of generally equal length rollers carrying lengths of material, the rollers having parallel axes of rotation, is well known. Such apparatus are seen in Gustafson (U.S. Pat. No. 3,767,510) and Karl (U.S. Pat. No. 3,004,694). The roller apparatus of Gustafson utilizes feed rollers that are positioned so that a laminated product of width equal to that of the material being fed from the plurality of feed rollers is produced. Karl uses various material widths and sequential feeding to form a container product. No provisions exists in either prior art reference for making a wider laminated product by joining several pieces of material along longitudinal edges thereof.
The joinder of material along longitudinal edges, without forming a laminated product, is seen in Bither (U.S. Pat. No. 1,410,879). In Bither, a pair of offset feed rollers feed cardboard through adjacent corrugated rollers to compress the edges of the cardboard being fed therethrough into a longitudinal seam. The adjacent rollers pinch the edges together to join the separate pieces of cardboard.
Cardinal (U.S. Pat. No. 4,050,972) shows lengths of material joined at the edge to form a blanket having a longitudinal seam. The blanket is laid over a playing field by a roller apparatus. The parallel pieces of plastic material overlap on the edges and are joined along the longitudinal seam by heat sealing or a similar process. Cardinal does not join the rolls of material together simultaneously as they are laid out, nor is a laminated product produced.
Mougin (U.S. Pat. No. 4,172,751) does utilize offset rollers which overlap at the ends thereof to join pieces of material together at the edge thereof. A separate strip of material is laid over the resulting seam to join two parallel lengths of material together. The separate strip is welded or sewn to the adjoining pieces of material. Mougin therefore uses a separate piece of material so that larger widths of material can be joined directly at the edge thereof, without overlap. The separate material is either welded or sewn to the two principal pieces of material, at a later time, not simultaneously or continuously. No laminate product is formed by the technique of Mougin. The resulting product is accumulated on a take-up drum for later utilization in insulating icebergs towed from antarctic seas to tropical waters.
The prior art does not show means for controlling longitudinal variation in separate pieces of material to be joined at or near an edge thereof. The patent to Gustafson shows a web guide for compensating for unevenly cut strips of material. No apparatus similar to Gustafson has been available in the art for maintaining a preselected overlap between adjacent pieces of parallelly extending lengths of material joined together at or near the edge thereof.
Though the use of adhesives in lamination is also well known, the use of an adhesive to simultaneously laminate layers as well as join parallel lengths of material together has not heretofore been utilized. Similarly, no method for evenly and uniformly applying the adhesive to the various pieces of material has been developed. The evenness of adhesive application is governed by the tension in the lengths of material being fed from their respective rollers to the primary take-up drum. The tension in the material itself is important in both uniform feeding of material and adhesive application. None of the prior art references show the use of variable tensioning to control feed as well as adhesive application.
A particular application of the product of the present invention is in insulated thermal blankets for covering prestressed concrete form beds. In a conventional manner, the form beds are adapted to receive a number of strands of pretensioned cable. The beds are then filled with concrete. Release of the tension in the strands, after setting and curing of the concrete, makes a strong and light prestressed concrete product. In order to maintain proper quality of the concrete, as well as maintaining a daily production rate, once the concrete is poured, the common practice is to apply heat to the beds for a period of eight to twelve hours to cure the concrete. As a matter of energy conservation, and expense savings, thermal blankets reduce the required amount of heat.
Previous practice has been to utilize a medium layer between two outer layers to form a laminated thermal blanket to cover the concrete in the form beds. Because the form beds are generally eight to fifteen feet in width and four hundred feet long, commercially available vinyl outer layers must be spliced together to cover the beds. The widths of the vinyl outer layers is four and one half feet to five feet. Therefore, prior practice is to make either a large number of separate blankets to cover the form beds, or to make a continuous blanket, with increased thermal efficiency, by sewing or heat sealing strips of material together in layers in a crosswise fashion relative to the length of the bed. This means a single blanket can have as many as one hundred seams running transverse to the length of the bed. The handling of material lengths of four hundred foot length has, until now, prevented the use of longitudinal seams.